Junichi Kinoshita

Transient chirping in distributed-feedback (DFB) lasers: effect of spatial hole-burning along the laser axis

An analysis of the chirping behavior of directly modulated distributed-feedback (DFB) lasers which takes into consideration the effects of spatial hole-burning along the laser axis is discussed. Rate equations including these effects are derived. To calculate the rate equations, the threshold condition of phase-shifted DFB lasers with a nonuniform refractive index distribution is analyzed. The calculations are carried out on phase-shifted DFB structures under the condition of random nonreturn to zero modulation at 1.8 Gb/s. The results show that the spatial hole-burning along the axis significantly affects the chirping behavior, adding to the effects induced by the spectral hole-burning alone. >

Yield analysis of SLM DFB lasers with an axially-flattened internal field

The results of the yield analysis of distributed-feedback (DFB) lasers which can operate in a single longitudinal model (SLM) are presented. A DFB structure with two lambda /8 phase-shifters is analyzed, together with conventional structures with no shifters and a single shifter. The SLM yield is defined such that the lasers satisfy the criteria of both normalized threshold gain difference ( Delta alpha L) and a flatness factor of the internal field profile along the cavity direction. Flattening the field profile is indispensable to minimize the effect of spatial hold-burning. The SLM behaviour of the double lambda /8 shift DFB lasers with ideally zero reflectivity facets is also analyzed as a parameter of the distance between the shifters ( Delta L). >

Five-wavelength integrated DFB laser arrays with quarter-wave-shifted structures

Five-wavelength integrated DFB laser arrays with quarter-wave-shifted structures, using nonuniform stripe width, have been developed for high-density WDM systems around the 1.3 μm wavelength region for the first time. Each DFB laser of the five-wavelength integrated DFB laser array oscillated at the Bragg wavelength with a side mode suppression ratio of more than 30 dB. Good reproducibility of 50 ± 5 A lasing wavelength separations has been obtained.

Performance of 1.5 mu m DFB lasers with a narrow stripe region

The performance of distributed feedback (DFB) lasers with a narrow region in the middle of the waveguiding strip and antireflective(AR)-coated facet ends is presented. The narrow region is designed to act as a three-quarter wavelength phase shift. Single longitudinal mode (SLM) capability is discussed both theoretically and experimentally. Calculated results predict the shift region is effective in relaxing axial hole burning because of a dip at the center of the axial field profile and a smaller optical confinement factor in the region. Experimentally, stable SLM operation up to more than 50 mW, a sidemode suppression ratio of more than 40 dB, and 3 dB modulation bandwidth over 10 GHz are achieved. >

Modeling of high-speed DFB lasers considering the spatial holeburning effect using three rate equations

A new approximated method of analyzing the effect of spatial holeburning on dynamic response of distributed feedback (DFB) lasers is proposed. This method consists of a mode-stability analysis based on the coupled-wave theory and a dynamic analysis utilizing only three spatially independent rate equations. The rate equations can be solved using the calculated result of the stability analysis. The stability analysis predicts that the break of stable single-longitudinal mode (SLM) operation will occur before the modal threshold gain reaches the value for the next mode. Based on this method, calculated results of de characteristics, large-signal responses, and AM responses, including harmonic distortion, are presented. >

Analysis of radiation mode effects on oscillating properties of DFB lasers

The effects of radiation mode on the oscillating properties of distributed feedback (DFB) lasers with second-order corrugations are analyzed for designing a new type of DFB laser. A formulation based on the transfer matrix technique is applied to calculating Streifers /spl zeta/-terms added to the coupled-wave equations. These terms represent the effects of radiation and evanescent modes. This formulation greatly simplifies the analysis of distributed resonance along multilayered waveguide structures with arbitrary-shaped second-order corrugations. The effects of vertical resonance are also incorporated into the formulation. Various types of DFB lasers with phase-shifted second-order corrugations are analyzed using this method. It is found that the phase shift and the blaze of the corrugations greatly affect the longitudinal mode selectivity. A new phase-shift DFB laser structure with two complementary blazing regions connected at the shift is proposed. It is demonstrated that this structure has small radiation loss resulting in low-threshold performance despite employing second-order corrugations.

Axial profile of grating coupled radiation from second-order DFB lasers with phase shifts

Axial profiles of the grating-coupled radiation field emitted in a direction normal to the surface of distributed-feedback (DFB) lasers with phase-shifted second-order corrugation are theoretically analyzed. The profiles are calculated for nonreflecting DFB lasers with the following phase shifts: lambda /4 shift, two lambda /8 shifts, and two 3 lambda /8 shifts. It is demonstrated that the radiation field can be controlled by changing the phase shifts. This result suggests a new method for modulating the surface emission of a DFB laser. >

53.3: New Light-bar Emitting Phosphor-converted White Line Light Pumped by InGaN/GaN Laser Diode for Edge-lit Backlight Unit Applications

A new type of light bar using laser diode for LCD backlight applications is presented. It consists of six white line-emission units including a high-power InGaN/GaN laser diode (LD). The LD emits at around 400nm and pumps up phosphors coated on a glass light-guide stick in the line-emission unit. It is demonstrated that a prototype of new LD package is capable of more efficient thermal transfer than the conventional CAN-type ones. The LD light bar has the following advantages: 1) fewer light emitting elements, 2) longer continuous white line emission, 3) higher rate of heat transfer.

57.4: Thin Side‐Lit, Hollow‐Cavity Flat LED Lighting Panel for Ultra‐Uniform LCD Backlight Applications

A new and thin, FL2P(Flat LED Lighting Panel) with ultra-high-uniformity for LCD backlight is presented. It has a hollow-cavity structure consisting of a pair of LED/collimator units, a slightly curved bottom reflector and a top diffuser, without any planar light guide inside. It has a great advantage of making itself thinner, less weight and lower cost. The LED/collimator unit has a collimating cylindrical lens and a side-placed RGB LED array. The collimating lens is developed particularly for higher-coupling efficiency and narrower beam to achieve thinner structure and more excellent uniformity.

Analysis of TE/TM mode selectivity in DFB lasers with a phase-shift region

In phase-shift distributed feedback (DFB) lasers, there is limited suppression of the TM mode despite extremely large submode suppressibility. The TE/TM mode selectivity of a DFB laser structure with a nonuniform waveguide region as the phase shifter is analyzed. Calculations of the threshold gain difference between the TE and TM modes are performed using the effective index method and the coupled-wave theory. It is found that the TM mode suppressibility can be doubled by optimizing the dimensions of the phase-shift region. This structure overcomes the TM mode problem.<<ETX>>